Pathogen removal through biological filtration and quantitative microbial risk assessments for drinking water purification

Biological filtration is a novel concept for drinking water purification that allows for the colonization of rapid granular filters with native bacterial organisms in order to reduce organic compounds in the final treated effluent. There is little published material on the efficacy of these filters for the removal of pathogens, specifically protozoa such as cryptosporidium and giardia which are difficult to inactivate using chlorine disinfection. This study utilizes aerobic endospores as a surrogate for cryptosporidium to characterize the removal performance of biologically active filters. Biological filtration was shown to achieve 3-log10 removal. In addition, Quantitative Microbial Risk Assessments were conducted for 10 Canadian drinking water utilities. Several of these risk assessments were based upon filter performance estimates derived from aerobic spore removal results. Most utilities are below the 10 -6 DALY pp/yr risk threshold established by the World Health Organization.